#!/usr/bin/python3

score = input('请输入分数:')
try:
    score = float(score)
except ValueError:
    print('输入的不是数字')
    exit()

if score > 100 or score < 0:
    print('请输入0-100的数字')
    exit()
elif score >= 90 and score <= 100:
    print('A')
elif score >= 80 and score <= 89:
    print('B')
elif score >= 70 and score <= 79:
    print('C')
else:
    print('D')
